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Have you ever wished you could just turn off your sweet tooth to help you resist that third piece of pie? For people, the downside of the deliciousness of sugar is simply feeling really full or gaining weight, but for cockroaches, their sweet tooth can be deadly.

The poisoned baits people set to kill roaches in their homes lure the unsuspecting insects in with sugar. But it turns out that the selective pressure of delicious, deadly traps throughout the environment has led to the rapid evolution of cockroaches that avoid sugar. They turned the sweet tooth off—or rather redirected it so it now tastes bitter.

A team of researchers from North Carolina State University published research this week looking at how the German cockroach, Blattella germanica, was able to adapt so quickly when surrounded by tasty insecticide. Sweet baits became popular for roach control in the mid-1980s, but several years later scientists began noticing a new behavioral trait: aversion to glucose, the most common simple sugar. The trait is heritable, and cockroaches with it avoided the baits. In areas treated with these traps, the roaches without a sweet tooth had much better survival rates than the roaches that lacked this new adaptation.

Insects’ sense of taste comes from hair-like structures on the mouthparts that contain nerve cells called peripheral gustatory sensory neurons. Insects have four “tastes”—sweet, bitter, water, and salt. Typically, foods that trigger the sweet neurons led the insects to eat, while foods that trigger the bitter neurons cause them to avoid that food.

The scientists, Ayako Wada-Katsumata, Jules Silverman, and Coby Schal, suspected that a change in the bitter and sweet sensory systems led to the glucose aversion trait. When they compared the sugar and bitter sensitivities of the averse roaches with the wild type, they found that the glucose triggered the same neurons as caffeine — very bitter. However, both groups of roaches still ate fructose, another simple sugar molecule, at the same rates.

Sampling wild cockroaches, they found glucose-averse individuals in seven out of 19 populations. The sensory responses in the native cockroaches mimicked the lab experiments, with caffeine and fructose responses remaining normal and glucose triggering the bitter system instead of the sweet. This shows that a very similar glucose aversion mechanism arose in multiple populations.

What kind of mutation led to this adaptive behavior? The researchers suspect that one or more mutations modified the bitter sensing system to react to glucose. For populations surrounded by sweet poisons, this mutation offers a serious evolutionary advantage. However, growth and reproduction of the glucose-averse roaches is slower than the normal population, so the mutation only functions as an adaptation in the face of attempted pest control.

The more we try to poison the roaches, the greater the advantages of being a cockroach that thinks sugar tastes bitter, and the more common this mutation will become. We probably need to find a new type of insecticide.

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Kate Prengaman
Kate is a science and environmental reporter living in Yakima, Washington. She writes about everything from emerging energy technology to persistent environmental problems and she really likes plants. Emailkate.arsT@gmail.com//Twitter@kprengaman

So to lose weight, try poison. Got it. Will get back to you with results.

Well, from the human point of view, sugar is indeed a poison in large quantities (causing liver damage and Type II diabetes), but it doesn't very often kill during or before reproductive age, so humans are presumably only verrrrrrrrry slowly evolving away from the sweet tooth.

"The more we try to poison the roaches, the greater the advantages of being a cockroach that thinks sugar tastes bitter, and the more common this mutation will become. We probably need to find a new type of insecticide."

Probably just the bait. In this case it sounds like they should switch to fructose. Or, better, have some traps with glucose and some with fructose.

Cockroaches can't evolve a distaste for every food flavor, or they will die by starvation.

If cockroaches hate caffeine, why do I find a ton of them in a half-filled coffee mug left overnight on someone's desk?

I'm guessing the German type as the American is large, fat and generally likes to live outdoors. They also are more likely to be found solo. If you have German roaches, you have a bigger problem hiding beyond sight somewhere because there is never just one German cockroach. It also means they have a feeding source nearby and have moved in. So either you have a really nasty office break room or a neighboring business doesn't believe in cleaning their kitchen.

We need an insecticide that tastes sweet, savory, bitter, and salty then.

If they just avoid people food we would all be happy, I think.

So insecticide that is chocolate covered bacon?

Just beacuse they don't eat it - does not mean that they are not walking around or pooping all over it. Leaving watever germs and dsieases they carry. So awesome your candy is still sitting on the coutner - but now it has roach feces all over it - Yumm !

We just need a way to kill them with 100% effectiveness. I suggest lasers.

Nah, they just need to extend the experiment: two sets of roach motels, to breed a roach that doesn't eat either High Fructose Corn Syrup or Partially Hydrogenated Soybean Oil (possibly the later replaced with whatever the current "transfat replacement" is). Next thing, roaches will be unable to eat nearly all food available for human consumers.

How many generations till the roaches have a captive species to eat the food first? Something similar to how certain ants have aphids?

When you say "quickly evolve" and later only later clarify it was over several years and dozens of generations that certainly doesn't help the general misconceptions about evolutionary theory.

What? That's the definition of 'quickly evolve'.

Normally you expect it to take hundreds of years and millions of generations; but in this case the hard selection criteria (eat sugar and die), makes it that those that don't prefer sugar get a hefty advantage.

If it was known that roaches had taste for sweet and sour this should have known. The roaches which like the sweets would be drawn to the bait which would kill off the sweet loving roaches. This would leave the sour loving roaches to reproduce. This also happens with bacteria in the body. When an antibiotic is used to kill the bacteria if stopped to soon the bacteria that is more resistance is left to reproduce and these will be more resistant to the antibodies. A lesson that was learned a long time ago.